The Biology of a Cactus

Origins

• The cactus is a plant thought to have originated in southern Mexico and northern Central America, according to the Dalhousie Collection of Cacti & Other Succulents. The cactus can be found from the central and western regions of Canada and south to Central America and the Gulf Islands to Mexico. Throughout the history of the cactus the biology of the plant has evolved to replace the leaves of the plant with spines that use less water than a leaf system.

Spines

• The spines of the cacti are usually located around a small mound of tissue known as the areole. The growth of the spines can take two forms, which are central and radial spines. Centralized spines are located close to the areole, while the radial spines grow from the circumference of the areole. The long, sharp and rigid spines of a cactus are used to reduce the effect of grazing animals from feeding on the plant, while some species of cactus grow without spines but emit a toxic substance to repel grazers. The spines of the cactus also provide shade for the plant from the high temperatures and intense sunlight found in the arid environments it inhabits.

Shoots

• The shoots of the cactus are usually thick and made of soft, succulent tissues to allow a large amount of food nutrients and water to be stored within them. The epidermis of the cactus is covered with a thick, waxy cuticle that can reduce the amount of water lost through the exterior of the plant. The stem of a cactus can be in the shape of a column without shoots, or can be made up of branches coming from the central column.

Roots

• The root system of a cactus is usually shallow and grows over a wide area around the plant, allowing the maximum capture of water found in the form of rain that lands around each plant. Some species of cactus also contain a taproot, a long part of the root system that penetrates deeper into the soil to gain nutrients and water. The taproot also acts as an anchor to hold the plant in position. The cactus is commonly pollinated by flying insects that are attracted to colorful flowers that grow on the plant and bloom during the daytime.